ACS Science SMOV Update - 1
David Golimowski (2 June 2009)
ACS-R Optimization Campaign
•
•
•
•
Image and O-scope data analysis complete
Initial default setting of bias voltages, clock rails, and pixel
transmission timing satisfy all WFC performance predictions for
May 2009. No voltages changes resulted in statistically significant
improvements in any detector characteristics.
Parallel CTE is only characteristic that is “problematic” for science.
Insensitivity to clock rail settings indicates that CTE is dominated
by radiation damage, which can only be mitigated by lowering CCD
temperature.
Ops Request for Iteration 2 prepared with 1 change from Iteration
1 configuration:
Increase bias offset for DSI mode to move bias level in half-speed
readout mode away from ADC rail. (Iter 1 half-speed data showed
bias level of 1300 DN and read noise of < 2 electrons.)
ACS Science SMOV Update - 1
David Golimowski (2 June 2009)
ACS-R Optimization Campaign
•
Iteration 2 begins just before midnight tonight EDT.
•
Investigating change for Iteration 3: mage and O-scope data
analysis complete
Change CEB-R → MEB data transmission settings to explore
possible slight improvement in RN by reducing feedthrough during
pixel integration.
•
OC Iterations 5 through 8 will be dropped.
Visit Group F: Science Data Transmission
Read Noise (DSI, Amp B, gain=2)
Noise vs Transmission Settings (AMP B)
PRESCAN
IMAGE
PRESCAN
IMAGE
7.000
y = -0.0004x + 5.8535
NOISE (e-)
6.000
5.000
4.000
3.000
y = 0.0012x + 3.9012
2.000
EXPID
New default for Iter 2 (BITS = 1, PREDELAY = -4, MIDDELAY = 6)
ACS-R Performance Summary
Metric
Jan 2007
(actual)
May 2009
(predicted)
Problematic
May 2009
(OC Iter 1)
Read noise
(e-; gain = 2)
C&S: 5.5
DSI: 4.0
10
DSI: 4.0-4.8
C&S: 4.4-5.7
Dark current
(e-/pix/hr)
10.7
15
100
20-25
Hot pixels (%)
0.68
1.1
1.5
1.1
Full well depth (e-)
84,000
84,000
40,000
~80,000
Non-linearity (%)
< 0.1
< 0.1
0.5
TBD
Parallel CTE
(EPER,1620 e-)
0.999949
0.999921
0.9999
0.99989
Cross-talk
4x10-5
4x10-5
4x10-4
1x10-4
Bias shift
(% after correction)
< 0.01
< 0.01
0.02
DSI: 0.02-0.30*
C&S: 0.01-0.02
* Values before digital correction. Teledyne algorithm corrects shift to < LSB, which
satisfies science criterion.
WFC1 – Dark Current
12 hr anneal 6 hr anneal
-77 C -81 C
WFC2 – Dark Current
12 hr anneal 6 hr anneal
-77 C -81 C
Visit Group A: Performance Summary
Hot pixel Parallel CTE (DSI, gain=2)
Visit Group A: Performance Summary
Hot pixel Serial CTE (DSI, gain=2)